Q1: It depends on why I passed which should be noted in my pass email. If I passed because of the concept, and that remains the same - then don't re-query. However, if I passed because the writing needed work and it's been revised, then yes.
Q2: My clients.

Your agent will then submit you to editors, who work for imprints in publishing houses. The editors will read and pass for the entire imprint, but not the entire publishing company, or they will offer and your agent will negotiate the deal for you. In a nutshell.

As long as you retain copyright of the work, this should not work against you. This should be considered a plus.

I take them in order.

I'd put it in the query for sure! It might not make ALL the difference, but it may make some.

Sometimes the MS starts out great and then kinda falls apart or I've lost interest while reading it. Or, I've researched editors and pub houses and realized the MS isn't as hot a commodity as I'd hoped. Or, the author is a jerk on social media. Many reasons.

Ask them for recommendations on if they feel the manuscript is ready for querying, and if so, what agents and/or agencies would this agent recommend you query. Ask anything you can do to make the manuscript more marketable. Ask about timelines and what are realistic expectations.

YA Contemp at 100k is a bit much. I'd keep it around the 75k or less marker, if you want my honest opinion. You might be able to get away with 85k if it's supernatural?? But 100k? Ooof. That's going to be a tough sell.

It does happen! We've got a company chat group where we toss up the query we like but can't rep for one reason or another, and the other agents tag it if they want a referral.
It's not daily, but it does happen.

Nope.
Still moving like molasses.
Sorry.

I've signed clients both ways.
I'd have to say, now, if I think the MS needs more work, I'm more inclined to offer a Revise and Resubmit first, before offering rep, to see how the writer handles revisions.

I'd say before.
Get out all the kinks and smooth out as much as you can before sending it to editors, be them freelance or from a pub house. A great beta reader can make ALL THE DIFFERENCE. They're seriously worth gold if you've got a good one.
Treat them well.

Specifically I'll be looking for:
BIPOC Horror
Mystery: especially Police Procedural
Thrillers: all kinds
Women's Historical: sweeping/romantic, supernatural twist OK: think Susanna Kearsley/Kate Morton
Science Fiction/Fantasy: unique trope twists and compelling emotional arcs

Even if I have, it's not your fault you didn't see my answer!
Auto-rejects:
Flirting in query.
Violence against women as plot devices.
Nazis of any kind. Hate em. Don't care.
Bashing on other books in a query.

Q: What happens if the agent dies / retires / disappears?

A: AAA code of practice says member agencies will make "provision for the protection & disbursement of clients’ monies in the event of... agent’s resignation, retirement, incapacity or death"

#AskAgent 7/7

Q: Does the agency commit to keeping you apprised of relevant information and offers received?

A: They should. It's your work; you should know who is reading it and any feedback.

#AskAgent 6/7

Q: Does the agency commit to keeping your confidential affairs confidential?

A: Ask for references to check the literary agency is trustworthy and reputable. And ask to see the privacy policy if it not clear in the agency agreement.

#AskAgent 5/7

Q: Are there any conflicts of interest?

A: There shouldn't be. Your literary agency should be only representing your best interests.

#AskAgent 4/7

Q: Does the agency have adequate professional insurance?

A: Literary agencies should have adequate professional indemnity insurance.

#AskAgent 3/7

Q: Will the agency pass on royalties and advances to you promptly?

A: AAA member literary agencies commit to this best practice: "use best efforts to transfer all sums due to the client within 10 days... but no more than 21 days in exceptional circumstances"

#AskAgent 2/7